Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session B40: 2D Magnetics II |
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Sponsoring Units: DMP Chair: Emily Been, Stanford University Room: Room 232 |
Monday, March 6, 2023 11:30AM - 11:42AM |
B40.00001: Coercivity enhancement induced by substitutional Ni-dopin in van der Waals Ferromagnet Fe3GaTe2 Hyobin Ahn Magnetic properties of well - defined crystals can be effectively tuned via substitutional doping of their magnetic core with other magnetic elements. In magnetic van der Waals (vdW) metal group FeXGeTe2 (X=3, 5), substitutional doping of Fe to other transition metal elements such as Ni, Co induces the transition of crystal’s magnetic properties, which offers wider range of material pool for exploring physical phenomena in vdW magnet as well as applications. Although doped FeXGeTe2 has been intensively researched for recent few years, doping effect of recently reported vdW ferromagnet Fe3GaTe2 hasn’t been reported yet. Here, we present the coercivity enhancement induced by substitutional Ni doping in Fe3GaTe2. Doping-induced coercivity enhancement is also reported in Co-doped Fe3GeTe2, which replaced ~58% of Fe with Co. This replacement decreases the curie temperature, from 220K to ~50K, which seems not adequate for applications. In our results, only small amount of Ni doping leads to dramatic increase of the coercivity of bulk crystal from 0.02T for un-doped one to ~0.7T. We speculate that the enhancement mainly originates from domain-wall pinning at Ni site, and further study is needed to clarify effects from other factors that are correlated to magnetic characteristic in metallic system, such as structural deformation, electrical doping, magnetic anisotropy energy, and etc. |
Monday, March 6, 2023 11:42AM - 11:54AM |
B40.00002: Anomalous Hall Effect in 2D Fe3GeTe2/Heavy Metal Heterostructures Stasiu T Chyczewski, Ji Shi, Kai Xu, Wenjuan Zhu Among the most promising candidates for practical spintronic designs are current-controlled magnetic devices such as spin-transfer torque (STT) and spin-orbit torque (SOT) devices. One major challenge however is the low power switching of the ferromagnetic (FM) layer, with van der Waals (vdW) ferromagnetic materials such as Fe3GeTe2 (FGT) representing a promising avenue to mitigate this issue. Materials in this new class offer a multitude of novel properties such as large anomalous Hall angles and spin polarizations that make them desirable for device applications. While some previous work has successfully demonstrated efficient SOT driven switching in FGT/platinum heterostructures, emergent magnetic properties of these structures have yet to be probed in depth. Here, we investigated FGT/heavy metal (HM) heterostructures using the anomalous Hall effect (AHE). We show that structures prepared using transfer can exhibit new behavior which we attribute to magnetic proximity effects at the FM/HM interface. New features include enhanced coercive fields and tails in measured hysteresis loops compared to devices that contain only FGT. These results differ notably from devices presented elsewhere in which the heavy metal was sputtered directly onto FGT. These results indicate that the quality of the FM/HM interface has significant impact on the properties of the vdW magnets and the SOT devices. |
Monday, March 6, 2023 11:54AM - 12:06PM |
B40.00003: Multiferroic metal with huge polar distortion driven by spin ordering: monolayer Fe3GeTe2 Jisoo Nam Classical and quantum electrodynamics show that the simultaneous existence of both ferroelectric instability and free electrons in a single-phase material is contradictory. However, it has been suggested that decoupling between softening transverse optical phonon mode and the free electrons might allow the coexistence of electric polarization and free electrons a few decades ago, thus they are called polar metal. In exploring numerous polar metal candidates, a rule of thumb is to look for a material where the atom for polar displacement and the atom for free electrons are distinct. In this work, we study a polar metallic behavior in a two-dimensional material composed of an odd number of layers. In this system, by using the first-principle calculations, the mirror symmetry breaking which originates from the spin configuration is possible without destroying the metallicity. Intriguingly, the single atom is responsible for both polar distortion and free electrons, thus a new class of polar metallicity. We demonstrate that the Fe3GeTe2 monolayer with three layers of Fe with broken mirror symmetry due to the spin configurations could show polar metallic behavior. The formation of ferroelectrics by magnetism in low-dimensional systems will open a new chapter in the discovery and application of new states of low-dimensional materials as a general method applied to all 2-dimensional materials and even several layers of metals. |
Monday, March 6, 2023 12:06PM - 12:18PM |
B40.00004: Study of Magnetic Structure and Magnetic Fluctuations in Cr4.74Te8 Single Crystals Mitchel Vaninger, Feng Ye, Xiaoqian Zhang, Guang Bian, Thomas W Heitmann, Alessandro R Mazza, Paul F Miceli There is extraordinary interest in developing metallic 2D van der Waals materials that exhibit ferromagnetism (FM) with perpendicular magnetic anisotropy. Cr4.74Te8 is one such system whose structure consists of layers of CrTe2 with extra Cr intercalated between them and it exhibits FM below Tc=160K. CrTe2 itself is known to be a strong ferromagnet up to room temperature [1]. Adding the intercalated Cr introduces additional magnetic interactions between the van der Waals layers. Recently it was reported that Cr4.74Te8 exhibits a large (10%) negative magneto-resistance effect above Tc, over a temperature range of 30K [2]. Neutron diffraction measurements performed on the CORELLI instrument at the Spallation Neutron Source reveal the presence of a modulated short-range magnetic phase with a wave vector perpendicular to the van der Waals layers and a period that is commensurate with three times the c-axis length. The existence of this modulated phase appears over the same 30K temperature range that is observed in the magneto-transport measurements. The results will be discussed in terms of the magnetic coupling that is introduced from the intercalated Cr layers. |
Monday, March 6, 2023 12:18PM - 12:30PM |
B40.00005: Collective Excitations in 2D Helimagnets Hung-Yu Yang, Gang Qiu, Abdullah Alrasheed, Fazel Tafti, Kang-Lung Wang In helimagnets, it is possible to find concurrent ferroelectric orders due to an interplay between spin-orbit coupling and helimagnetism. In such cases, apart from phonons and magnons, the systems may also host other types of collective excitations such as ferrons and electromagnons. Here, we employ inelastic electron tunneling spectroscopy to study nickel dihalides, which are 2D helimagnets with ferroelectric orders. We found signatures of collective excitations at meV scale. Besides, our results suggest that these excitations respond differently to an in-plane and out-of-plane magnetic field, in contrast to the magnons in 2D collinear magnets chromium trihalides. Our study paves the way for further characterizations of collective excitations in 2D helimagnets. |
Monday, March 6, 2023 12:30PM - 12:42PM |
B40.00006: Intrinsic exchange bias in van der Waals alloy Cr0.45Pt0.55Te2 Ryan Bailey-Crandell, Warren L Huey, Archibald . Williams, Joshua E Goldberger, Roland K Kawakami Two-dimensional van der Waals magnetic materials are of recent interest for scientific and technological applications. The novelty in two dimensional magnetic materials means there are new paradigms and functionalities that have yet to be explored, including atomically thick layered structures. Here we report evidence of a novel magnetic structure in exfoliatable van der waals magnetic alloy Cr0.45Pt0.55Te 2 (CPT). We use magneto-optic measurements to observe hysteresis loops in exfoliated CPT samples. The most notable attribute of CPT's hysteresis is that the loop is not centered at zero. We interpret this as an exchange bias effect, reminiscent of heterostructures of ferromagnets and antiferromagnets, but intrinsic to this material. We explain this effect as a layer-by-layer system of coupled ferromagnetic layers, exerting exchange bias on each other. This work demonstrates layer by layer exchange bias effects that pave the way for further understanding exchange in two dimensional systems. |
Monday, March 6, 2023 12:42PM - 12:54PM |
B40.00007: Optical detection of antiferromagnetic dynamics in CrCl3 Shekhar Das, Alex L Melendez, I-Hsuan Kao, Francisco Ayala Rodriguez, Simranjeet Singh, P Chris Hammel Nitrogen-vacancy (NV) centers in diamond and newly discovered Boron-vacancy (BV) centers in h-BN also known as color-centers provide a non-invasive and sensitive method to probe weak magnetic field fluctuations generated by magnons. Enabling the detection of magnetic dynamics at frequencies exceeding the color-center ESR frequency (typically a few GHz) is essential in order to probe the dynamics of many ferri- and antiferromagnetic materials. The recent discovery of optical detection of magnetic resonance occurring above the NV center ESR frequency reveals a route to the exploration of the antiferromagnetic spin dynamics [1,2]. The scattering of two high-frequency magnons, or two-magnon scattering, generates electromagnetic noise at their difference frequency which can match the color-center frequency enabling the detection of higher-frequency dynamics. Here, we show the optical detection of antiferromagnetic resonance in a bulk CrCl3 crystal. At 9 K, the optical branch resonates at 9 GHz, three times larger than the NV center ESR frequency. The temperature evolution of the resonance mode confirms that it originates from antiferromagnetic dynamics. Such dynamics can also be excited using spin-orbit torque (SOT) generated by current in an adjacent layer. The low in-plane symmetry of WTe2 generates an out-of-plane SOT component excites antiferromagnetic dynamics measured using NV/BV centers in diamond/hBN. |
Monday, March 6, 2023 12:54PM - 1:06PM |
B40.00008: Understanding the Anomalous Hall effect in Co1/3NbS2 with revised crystal and magnetic structures Greg MacDougall, Kannan Lu, Azel Murzabekova, Soho Shim, Junehu Park, Soyeun Kim, Lazar L Kish, Yan Wu, Lisa M DeBeer-Schmitt, Adam A Aczel, Andre Schleife, Nadya Mason, Fahad Mahmood A large anomalous Hall effect (AHE) has recently been observed in the intercalated transition metal dichalcogenide Co1/3NbS2 below a known magnetic phase transition at TN = 29 K. The magnetically ordered state is widely believed to be a form of collinear antiferromagnetism which preserves parity and time reversal symmetry, and there has been discussion about if and how such a state could lead to an AHE or whether the latter should be associated with a weak ferromagnetic moment seen immediately below the transition temperature. In this talk, I address this controversy by presenting new neutron diffraction data on single crystals of Co1/3NbS2 and an analysis which suggests that moments in the ordered phase stabilize in a non-collinear configuration. We further present new transport and magneto-optic Kerr measurements which demonstrate that the AHE persists in this material below TN to temperatures as low as T = 5 K. Finally, we show that AHE signatures in our sample are accurately reproduced by density functional theory calculations. These collective results firmly associate the anomalous transport signatures with the antiferromagnetically ordered state in this material and lends credence to the crystal Hall effect picture. |
Monday, March 6, 2023 1:06PM - 1:18PM |
B40.00009: spds* tight-binding calculation of the local density of states near vacancies in wurtzite GaN Joseph Sink, Michael E Flatté GaN has become ubiquitous in modern technology due in part to its large direct band gap (~3.4eV) which makes it ideal for use in blue LEDs and high field power electronics, as well as its high displacement energy which makes it `naturally’ radiation hardened when compared with Si and GaAs[1]. While there has been significant experimental effort dedicated to the effects of impurities and radiation induced defects at the device level, much less is known about the electronic properties of single defects. We describe an approach to calculating the effects of impurities in bulk crystals by using an spds* (with spin-orbit coupling) tight-binding Green's function formalism. In this approach, the real-space homogeneous Green's functions are constructed by numerically Fourier transforming the k-space propagator. This method has been successfully applied to transition metal impurities in zincblende GaAs [2, 3]. We treat gallium and nitrogen vacancies in wurtzite GaN by perturbatively decoupling the vacancy atomic site from its neighbors and then setting a large onsite potential. We present results for the real-space local density of states as well as topological scans for m- and a-plane wurtzite GaN. |
Monday, March 6, 2023 1:18PM - 1:30PM |
B40.00010: Database of Computed Properties for Color Center Defects in Silicon Vsevolod Ivanov, Alexander Ivanov, Jacopo Simoni, Prabin Parajuli, Liang Tan, Thomas Schenkel Color center defects in silicon are emerging as a promising platform for realizing a number of |
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